1. Field of the Invention
The present invention generally relates to prism sheets, and particularly, to a prism sheet used in a liquid crystal display (LCD).
2. Discussion of the Related Art
The weight and thinness of liquid crystal display panels make them suitable for a wide variety of uses in electronic devices such as personal digital assistants (PDAs), mobile phones, portable personal computers, and other electronic appliances. Liquid crystal is a substance that does not illuminate light by itself. Instead, the liquid crystal relies on light received from a light source to display information. In a typical liquid crystal display device, a backlight module powered by electricity supplies the needed light.
FIG. 7 is an exploded, side cross-sectional view of a typical liquid crystal display device 100 employing a typical prism sheet 10. The liquid crystal display device 100 includes a housing 11 and a plurality of lamps 12 positioned in the housing 11. The liquid crystal display device 100 further includes a light diffusion plate 13, a prism sheet 10, and a liquid crystal display panel 15 stacked on the housing 11 in that order. The lamps 12 emit light, and the inside walls of the housing 11 are configured for reflecting some of the light upwards. The light diffusion plate 13 includes a plurality of embedded dispersion particles. The dispersion particles are configured for scattering received light, and thereby enhancing the uniformity of light that exits the light diffusion plate 13. Also referring to FIG. 8, the prism sheet 10 includes a base layer 101 and a prism layer 102 formed on the base layer 101. The prism layer 102 has a plurality of V-shaped structures 103. The V-shaped structures 103 are configured for collimating, to a certain extent, the received light.
In use, unscattered light from the lamps 12 enters the diffusion plate 13 and becomes scattered. The scattered light leaves the diffusion plate 13 to the prism sheet 10. The scattered light then travels through the prism sheet 10 and is refracted out at the V-shaped structures 103 of the prism sheet 10. Thus, the refracted light leaving the prism sheet 10 is concentrated at the prism layer 102 and increases the brightness (illumination) of the prism sheet 10. The refracted light then propagates into a liquid crystal display panel (not shown) disposed above the prism sheet 10.
However, a typical method of manufacturing the prism sheet 10 includes the following steps: first, a melted ultraviolet(UV)-cured transparent resin is coated on the base layer 101 to form V-shaped lenses, then the melted ultraviolet-cured transparent resin is solidified to form the V-shaped structures 103. This results in that the V-shaped structures 103 of the prism layer 102 are usually damaged or scratched due to their poor rigidity and mechanical strength.
In addition, the V-shaped structures 103 are generally regularly arranged and extend along a direction parallel to one edge of the prism sheet 10. The V-shaped structures 103 are prone to be aligned similarly to pixels of the liquid crystal display panel 15, consequently, moiré patterns may occur between the prism sheet 10 and the pixel pitch of the liquid crystal display panel 15. In order to reduce or eliminate the moiré patterns and protect the V-shaped structures 103 of the prism sheet 10, the liquid crystal display device 100 should further include an upper light diffusion film 14 on the prism sheet 10. However, although the upper light diffusion film 14 and the prism sheet 10 are in contact with each other, a plurality of air pockets still exist at the boundary between the light diffusion film 14 and the prism sheet 10. When the liquid crystal display device 100 is in use, light passes through the air pockets, and some of the light undergoes total reflection at one or another of the corresponding boundaries. In addition, the upper light diffusion film 14 may absorb an amount of the light from the prism sheet 10. As a result, a brightness of light illumination of the liquid crystal display device 100 is reduced.
Therefore, a new prism sheet is desired in order to overcome the above-described shortcomings.